IMPROVEMENTS RELATING TO BONDED PANEL STRUCTURES

Abstract: A bonded panel for use as an interior panel for a car body comprises a central or core layer (C), and outer and inner layers (A, B) sandwiching the core layer. All three layers comprise as the main constituent thereof a layer (4) of heavy duty paper, conveniently Kraft, typically having a weight of about 125 gms per sq. meter. The inner and outer layers are provided with vent holes (10), to allow gases produced during the moulding of the panel to be vented. Conventionally, attached to the outer layer (A), by a layer (2a &cir& _) of adhesive, is a decorative layer, the adhesive layer (2a &cir& _) effectively sealing the vent holes (10a &cir& _) in the outer layer. Provided on the layer (6) of Kraft of the core (C), on the side thereof adjacent to the inner (undecorated) layer (B) is a layer (7) of aluminium foil, preventing the integrity of the core being damaged in the event of warm moist air entering the space between the layers (A and B) through the vent holes (10b &cir& _) in the inner layer.

Description: Title: "Improvements relating to bonded panel structures" Description of Invention This invention is concerned with improvements relating to bonded panel structures. A conventional bonded panel comprises a corrugated or fluted core (hereinafter referred to as "fluted" for convenience), conventionally comprising heavy-duty paper such as Kraft, and inner and outer layers, conventionally also comprising heavy-duty paper such Kraft, bonded to the core by a heat-softenable adhesive such as polyethylene. Such a conventional bonded panel (hereinafter referred to as being of the kind specified) may be moulded by the application of heat and pressure, the inner and/or outer layers slipping over the core whilst the moulding takes place, and the adhesive sets on cooling with the panel in its moulded configuration. Examples of such conventional bonded panel structures may be found in British Patent Specification Nos. 2004810, 2038707, 2029755, 1576396, 1558150, 1575663, 1582539, 1548807, 1532762, 1554073, 1576546, 1576142, 1555882, 1501027. Such a bonded panel is conventionally used on the interior of motor vehicles, the inner layer being attached, such as by the use of adhesive, by ties, by clips or simple press-fitting as is disclosed in the above-mentioned patent specifications, to the vehicle body surface, and the outer layer being covered by a decorative layer. During moulding hot gases such as steam are created, and need to be vented, and for this purpose a large number of small vent holes (conventionally termed "prickle" holes) are provided, conventionally at about 3cm separation, extending completely through the panel, including the core material. During moulding, the exhaust gases are vented through exhaust apertures in one of the two dies. During finishing of the panel, the vent holes on the outer layer may be sealed with adhesive by which the decorative layer is attached, but not so the inner layer. In use, the panel may be subjected to extreme environmental conditions, including being subjected to heat and humidity. A conventional bonded panel of the kind specified tends to fail under conditions of high humidity, since hot moist air may enter the interior of the panel through the vent holes, and weaken the corrugated layer, reducing the strength or stiffness of the panel. Specifically all car components are subjected to an environmental cycling test which includes the following: a) subjecting the panel to a high temperature at normal humidity for several hours; b) subjecting the panel to a very low temperature and medium humidity for several hours; and c) subjecting the panel to a medium temperature and high humidity for periods up to 24 hours. According to this invention there is provided a bonded panel comprising a fluted core, and outer and inner layers secured thereto by adhesive, wherein the core comprises a layer of aluminium foil. Preferably the layer of aluminium foil is provided on the side of the core adjacent to the inner layer, i.e. opposite to that to which a decorative layer will be secured. Preferably vent holes are provided extending through the outer and inner layer only, and do not extend to the core layer. In this manner moisture will be prevented from entering the core layer through the outer layer, by virtue of the adhesive by which the decorative layer is secured to the outer layer, and the layer of aluminium foil will protect the core layer from the effects of humidity entering through the vent holes provided on the inner side. Thus where the fluted cores comprises a layer of heavy duty paper such as Kraft, preferably the aluminium layer is bonded thereto on the side thereof adjacent to the inner layer of the panel. Preferably the layer of heavy duty paper has a weight within the range 80-150 gms/sq.meter. If desired however the fluted layer may comprise a layer of lighter weight paper on the inner side of the aluminium layer, e.g. of Kraft paper, conveniently having a weight within the range 40-70 gms/sq. meter. Desirably the aluminium foil is between 6 and 50 microns preferably lying between 12 and 28 microns, most desirably about 18 microns in thickness. Thus where a decorative layer is provided on the outer side by adhesive, said adhesive preventing the hot humidified air to which the panel is subjected during environmental testing from entering the core through the vent holes, the aluminium layer preventing hot humidified air which enters through the vent holes of the inner layer from weakening the fluted layer. However if desired a layer of aluminium foil may be provided on both sides of the core material, although under such circumstances the thickness of aluminium which will be used will be at the lower end of the range given above, or less, e.g. between 4 and 18 microns. The invention is particularly useful in bonded panels of the kind comprising layers of Kraft affording the major components of both the inner and outer layers, such as is described in the above-mentioned patent specifications. There will now be given a detailed description, to be read with reference to the accompanying drawings, of a bonded panel structure which is a preferred embodiment of this invention, having been selected for the purposes of illustrating the invention by way of example. The accompanying drawing is a schematic sectional view of part of the bonded panel which is the preferred embodiment of this invention. The bonded panel shown in the drawings is for use as an interior panel for a car body, comprising a central or core layer C, and outer and inner layers A and B, sandwiching the core layer. Both the outer and inner layers comprise as the main constituent thereof a layer 4 of heavy duty paper such as Kraft, typically of a weight of about 125 grams per square metre having on its interior face a layer 5 of polyethylene adhesive, and being bonded to the layer of Kraft on the side thereof remote from the core by a layer 3 of polyethylene adhesive, a layer 2 of Kraft paper, typically of 50 grams per square metre in weight, and each of the inner and outer layers is provided with a plurality of vent holes 10. The core layer C comprises, as is conventional, a corrugated or fluted layer 6 of Kraft, also having a weight at about 125 grams per square meter affording in conventional manner the majority of the strength of the panel, and a layer 8 of Kraft paper. Also in accordance with conventional practice, the inner layer only is completely bonded to the core layer at the contact areas therebetween by the layer 5 of adhesive, the outer layer being bonded primarily only along the edges thereof, allowing the outer layer to slip over the core layer during deformation whilst the moulding process is carried out. In accordance with this invention there is interposed between the layer 6 and the layer 8 of the core a layer 7 of aluminium foil, said layer being approximately 8 microns in thickness. In this way the layer of Kraft in the core is protected against heated humidified air entering the core area through the prickle holes 10 in the inner side B, during environmental testing. When the panel is moulded and the layers 5 of polyethylene softened, desirably the thermo-forming is carried out without simultaneously sealing the edges, to allow gases to vent longitudinally of the corrugations. Whilst the invention has been described above in relation to a conventional bonded panel for use in the moulding of an interior panel for a vehicle, the invention may be applied where similar problems arise, albeit in relation to a laminated panel of different constructions, for example in the provision of shelf panels. The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims: CLAIMS 1. A bonded panel comprising a fluted core (C), and outer and inner layers (A, B) secured to the core by adhesive, wherein the core comprises a layer (7) of aluminium foil. 2. A bonded panel according to Claim 1 wherein the layer (7) of aluminium foil is provided on the side of the core adjacent to the inner layer (B). 3. A bonded panel according to one of Claims 1 and 2 wherein vent holes (10a, 10b) are provided extending through the inner and outer layers (A, B) only. 4. A bonded panel according to any one of the preceding claims wherein the fluted core (C) comprises a layer (6) of heavy duty paper. 5. A bonded panel according to Claim 4 wherein the layer (6) of heavy duty paper has a weight within the range 80-150 gms/sq. meter. 6. A bonded panel according to one of Claims 4 and 5 wherein the fluted layer (C) comprises a layer (8) of light weight paper, conveniently having a weight within the range 40-70 gms per sq.meter. 7. A bonded panel according to any one of Claims 4, 5 and 6 wherein the aluminium layer (7) is bonded to the fluted layer (C) on the side of the heavy duty layer (6) thereof adjacent to the inner side of the panel. 8. A bonded panel according to any one of the preceding claims wherein the layer (7) of aluminium foil is between 60 and 50 microns in thickness, preferably lying between 12 and 28 microns. 9. A bonded panel according to any one of the preceding claims comprising a decorative layer provided on the outer side (A) by adhesive, said adhesive preventing hot humidified air to which the panel is subjected from entering the core through the vent holes (10a), the aluminium layer (7) preventing hot humidified air which enters the vent holes (10b) of the inner layer (B) from weakening the fluted layer (C).

Inventors: CHO KUNIO, GRAY HENRY BERNARD, OGATA MITSUGOSHI, CHO, KUNIO, GRAY, HENRY, BERNARD, OGATA, MITSUGOSHI
Applicants: CHO KUNIO, EFTEN EUROPA BV, GRAY HENRY BERNARD, OGATA MITSUGOSHI, CHO, KUNIO, EFTEN EUROPA B.V., GRAY, HENRY, BERNARD, OGATA, MITSUGOSHI
Application year: 1994
Main classification: B32B3
IPC codes: B32B3, B60R13